Hemagglutination of neuraminidase-treated human erythrocytes by Leishmania enriettii infected guinea-pig sera.

Sera from guinea-pigs infected with the protozoan parasite Leishmania enriettii showed higher hemagglutination (HA) titres for neuraminidase treated human erythrocytes than those of normal guinea-pig sera. This HA activity was associated mostly with the 19S fraction of the immune serum and could be absorbed out with an antigenic fraction of the parasite membrane. Antigenic determinants involved in this HA reaction consisted of, at least, beta-D-galactosyl or lactosyl residues.     

Failure to produce tumours in cattle with 20-methylcholanthrene and 3,4-benzpyrene

Zusammenfassung Fünf jungen Kälbern wurden chemische Karzinogene (20-Methylcholanthren und 3,4-Benzpyren) subkutan oder mittels implantierter Gelatinekapseln verabreicht. Die Tiere wurden 6–36 Monate lang beobachtet. In keinem der Tiere konnten signifikante Veränderungen festgestellt werden.     

Hemagglutination of neuraminidase-treated human erythrocytes byLeishmania enriettii infected guinea-pig sera

Summary Sera from guinea-pigs infected with the protozoan parasiteLeishmania enriettii showed higher hemagglutination (HA) titres for neuraminidase treated human erythrocytes than those of normal guinea-pig sera. This HA activity was associated mostly with the 19S fraction of the immune serum and could be absorbed out with an antigenic fraction of the parasite membrane. Antigenic determinants involved in this HA reaction consisted of, at least, -d-galactosyl or lactosyl residues.     

Triterpenes ofAlstonia scholaris (dita-bark)

Résumé Le triterpène majeur de l'écorce d'Alstonia scholaris est identifié comme acétate d'-amyrine et acétate de lupéol.     

Attentional modulation in visual cortex depends on task timing

Paying attention to a stimulus selectively increases the ability to process it. For example, when subjects attend to a specific region of a visual scene, their sensitivity to changes at that location increases. A large number of studies describe the behavioural consequences and neurophysiological correlates of attending to spatial locations. There has, in contrast, been little study of the allocation of attention over time. Because subjects can anticipate predictable events with great temporal precision, it seems probable that they might dynamically shift their attention when performing a familiar perceptual task whose constraints changed over time. We trained monkeys to respond to a stimulus change where the probability of occurrence changed over time. Recording from area V4 of the visual cortex in these animals, we found that the modulation of neuronal responses changed according to the probability of the change occurring at that instant. Thus, we show that the attentional modulation of sensory neurons reflects a subject's anticipation of the timing of behaviourally relevant events.